Proton and phosphorus-31 nuclear magnetic resonance study of zinc(II)O,O′-dialkyl dithiophosphates in solution

Abstract

Proton and ³¹P n.m.r. have been employed to investigate the constitution and behaviour of zinc(II)O,O′-dialkyl dithiophosphates in solution. The complexes Zn[S₂P(OR)₂]₂(R = Et or Prⁱ) are principally dimeric in chloroform and toluene with dissociation constants, K_D(R, solvent), to monomers of 1.81 × 10^–2(Et, CDCl₃), 3.08 × 10^–2(Et, toluene), 4.45 × 10^–2(Prⁱ, CHCl₃), and 7.17 × 10^–2 mol I^–1(Prⁱ, toluene) at 29 °C. Higher ³¹P chemical shift values and conductance data for solutions of these compounds in ethanol and tetrahydrofuran indicate that co-ordination of solvent and ligand ionization occur in these solvents. The ³¹P chemical shifts for complexes Zn[S₂P(OR)₂]₂·L increase in the order L = pyridine < 2,2′-bipyridine < 2,2′: 6′,2″-terpyridine, and comparison with known structural data has shown that this change is due primarily to an opening of the SPS bond angle of the S₂P(OR)₂ ligands. The ‘basic’ zinc(II)O,O′-dialkyl dithiophosphates, Zn₄[S₂P(OR)₂]₆O, are unstable in solution, spontaneously, though reversibly, decomposing to ‘normal’ Zn[S₂P(OR)₂]₂ and zinc(II)oxide as the temperature is increased. Pyridine (py) causes an irreversible decomposition of Zn₄[S₂P(OR)₂]₆O to Zn[S₂P(OR)₂]₂·py and zinc(II).